Sensing switch

ABSTRACT

Disclosed herein is a sensing switch assembly for use with copying machines which is highly sensitive to passage of paper or other delicate sheet material and can operate to switch devices employing high electrical current without any sparking to effect the delicate sensing mechanism. Included is a roller element journaled in a spring arm and biased against a contact plate by the action of the spring arm. The spring arm and contact plate are in the loop of an electrical circuit which actuates further switching operations. When a piece of sheet material passes between the roller element and the contact plate, the contact between the element and plate is broken to open a switch in the circuitry. The electrical circuitry includes a transistor and when the switch is open, current is caused to flow from the base to the emitter of the transistor thus causing current to flow from the collector to the emitter of the transistor which operates to switch a large load in the circuitry of the transistor.

United States Patent [72] Inventor Guy Weber Dieppe, France [21] Appl. No. 815,355 [22] Filed Apr. 11,1969 [45] Patented June 29, 197! [73] Assignee La Cellophane Societe Anonyme Paris. France [32] Priority Apr. 12, 1968 [33] France [31] 147896 [54] SENSING SWITCH 5 Claims, 5 Drawing Figs. [52] U.S.C| 307/119, 200/ 1 66 [51] lnt.Cl ..H0lh 35/00 v [50] Field ol'Search 307/116, 117,l18.119,134;200/46,166B,166F

[56] References Cited UNITED STATES PATENTS 3,024,334 3/1962 Rhodes 200/166 8 2 3,274,368 9/1966 De Boo et a1 ZOO/166 F 3,006,450 10/1961 Nash 200/46 X Primary Eraminer Robert K. Schaefer ASSiSIGn!EIH!71iHf-H.J. Hohauser Almmey- Sherman and Shalloway ABSTRACT: Disclosed herein is a sensing switch assembly for use with copying machines which is highly sensitive to passage of paper or other delicate sheet material and can operate to switch devices employing high electrical current without any sparking to effect the delicate sensing mechanism. Included is a roller elementjournaled in a spring arm and biased against a contact plate by the action of the spring arm. The spring arm and contact plate are in the loop of an electrical circuit which actuates further switching operations. When a piece of sheet material passes between the roller element and the contact plate, the contact between the element and plate is broken to open a switch in the circuitry. The electrical circuitry includes a transistor and when the switch is open, current is caused to flow from the base to the emitter of the transistor thus causing current to flow from the collector to the emitter of the transistor which operates to switch a large load in the circuitry ofthe transistor.

PATENTED JUN29 IBYI sum 1 or 2 INVI'INTUR PATENTEUJUNZSIQYI 3,590,270

FIG. 4

FIG 5 E I Guy WERE R SENSING SWITCH BACKGROUND OF THE INVENTION Known sensing switches generally operate abruptly, that is to say, a slight mechanical pressure immediately causes the change in equilibrium of a strip or spring, causing the desired making or breaking of current. When these devices, of which the contact pressure is relatively low, have to serve to control relatively large currents, it is generally necessary to use a relay as an intermediate device.

The deformation of equilibrium of these sensing switch strip or springs which is sometimes linked to the stroke of a pusher, is not absolutely instantaneous. The mechanical precision of operation of these switches is thus low when they are used to detect positions, since the geometrical positions of a pusher relative to a sensing switch are often not the same for engagement and for disengagement. Furthermore, though the pressure required for operation is relatively low, it can be too great for certain applications, which however require the switching of a high potential. Such is particularly the case for document duplicating machines in which the precise and rigorous triggering of copy sheetsis determined by the passage of a simple sheet ofpaper which is frequently very thin.

The action of the sensing switches used in duplicating machines must be disengaged by an extremely gentle contact. These devices must be particularly sensitive while remaining insensitive to vibrations which can affect the machine. They must also function reliably while being substantial enough to switch high potentials.

SUMMARY OF THE INVENTION The present invention relates to sensing switches, that is to say, switches which, acting on mechanical information, have the effect of automatically making or breaking the current in an electrical circuit and thereby causing decisive effects, such as the stopping or starting of electrical motors, a change in their running, the operation ofsafety devices, etc.

According to the present invention, there is provided a sensing switch comprising a first contact in the form of a ball or other roller element mounted, preferably but not necessarily, for rotation, on a resilient, conducting strip and a second contact in the form of a conducting surface against which said ball or roller is resiliently urged by said strip. The second contact may be either flat, or convex to assume and emphasize the point contact between the two elements.

The sensing switch is used to control relays by the intermediates of a transistor amplifier acting as a binary switch with the potential of the current established by the contact of the ball with its support in the order of a few millivolts. This very low control potential avoids the spark erosion of the contacts, which seriously affects the sensitivity and precision of conventional sensing switches.

The contact between the ball or roller and the surface, which is strictly a point or line contact, is very precise and its sensitivity is only a function of the elasticity and resistance of the pieces of metal of which it consists. It can thus be as high as one wishes.

The ball or roller is arranged at the end of a metallic strip through which the current reaches it. The metallic strip is chosen to be as resilient as possible, strips of foil being perfectly suitable for this purpose. Their resilience, which can be made to increase progressively by using superimposed staggered strips, also makes it possible to control the contact pressure of the ball or roller on the surface of the second contact.

The insertion ofa sheet of paper between the ball or roller and the surface immediately opens the contact. Conversely, the contact is reestablished as soon as the sheet of paper is no longer interposed. It will be seen that whilst the contact has all the sensitivity desired, it remains completely insensitive to vibrations which can affect the machine, because of its resilience. If the plane of deformation of the strip is in the direction of travel of the paper furthermore great positional stability is achieved, thus bringing about perfect reproducibility of the switching operations from one sheet of paper to the next.

The sensing switch may be arranged as a shunt on one arm of a bridge which provides the base potential of a transistor acting as an amplifier. In practice, the transistor functions as a switching device. The making or breaking of the current of the bridge in the shunt circuit which is controlled by the sensing switch changes the base potential of the transistor and allows it to operate in the blocked state or conducting state and vice versa. When a sheet of paper passes through the microswitch the shunt is broken and the transistor base is at the operating potential. The transistor conducts and effectively makes a high power circuit. When a sheet of paper is no longer interposed in the microswitch, the base is retuned, to earth potential and the transistor is blocked.

While certain types of rolling ball contacts have been used in switching operations of the prior art, the present invention gives ball contacts a switching efficiency not previously available. The ball contact is required to break only a low potential current while its combination with the transistor amplifier permits the switching of heavy loads. The resulting efficiency of the ball contacts as employed in the present invention is unparalleled. Spark erosion of the ball contact is avoided while instantaneous response is achieved. The device is extremely sensitive yet rugged and capable of withstanding long hours of constant use.

It is, therefore, an object of this invention to provide an extremely efficient and highly sensitive switch.

It is a further object of this invention to provide a sensing switch for sensing the position of sheet material which can accurately and quickly respond to the position of such sheet material.

It is a further object of this invention to provide a sensing switch assembly which is simple to construct yet has a long life and high reliability.

It is still another object of this invention to provide a sensing switch assembly including a ball contact that can switch heavy loads in response to minute changes in the position of the ball contact.

Still another object of this invention is to provide a sensing switch assembly having a ball contact actuated by thin sheet material which can switch heavy loads without spark erosion of the contact.

It is a more specific object of this invention to provide a sensing switch including a ball contact rotatably mounted in a current-carrying strip which urges the ball against a contact plate and the switch created by the two contacts operating to control a transistor amplifier.

Another specific object of the invention is to provide a laminated metallic strip for carrying the ball contact and an adjustable pressure mounting for the ball contact.

Yet another object of the invention is to provide a sensing switch including a ball contact and a plate arranged to be actuated by sheet material with the switch of the ball and plate arranged as a shunt on one arm of a bridge which provides the base potential of the transistor acting as an amplifier.

Still another specific object of this invention is to provide a switch for controlling a copy machine wherein the power to the controlled load is supplied through a circuit including a transistor and the base potential of the transistor is controlled by a switch having ball and plate contacts.

These and other objects will become readily apparent upon consideration of the following description of a preferred embodiment when taken in conjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side elevation, in section, of one embodiment of sensing switch according to the invention;

PREFERRED EMBODIMENT Referring now to FIG. 1, there is illustrated a sensing switch including a ball 1 rotatably fixed for example, by crimping, at one end of a strip of foil 2. The strip is shown of laminated construction including a long strip 2a which actually carries the ball, 7 and shorter strips 2b, 20, etc., the strips being clamped by screws 9 to a contact 4.

The ball is urged by the resilience of the strip into contact with the upper surface of a conducting plate 3, which is mounted in an insulating table 5. The force with which the ball is urged against the plate 3 may be adjusted by rotating the contact 4 about the insulated mounting pivot 8, the contact 4 being locked by means of the screw in any desired position.

A guide 7 is spaced from the table 5 and feeds sheets of papers 6 or other insulating material to be detected, between the ball 1 and the plate 3. Electrical leads from the plate 3 and the terminal 4 are placed across the points E and B in one of the circuits illustratedin FIGS. 2 to 5, in each of which the transistor 11 has a potential divided AEB, the base being connnected to the center point E of the divider.

The basic circuitry of the embodiments of FIGS. 2 to 5 is the same, with different figures showing different arrangements for connecting the load that is to be controlled by the sensing switch. In each of the illustrated embodiments, resistors R and R are bias resistors which operate to control the transistor 11. When the switch across EB is open, current is caused to flow through resistors R-2 and R4 since the transistor will be biasedto a conducting state. When the transistor 11 is in the conducting state, a high current is caused to flow through R4, the current controlling the load of the copy machine for which the sensing switch is provided.

Each of the FIGS. 2 to 5 show different connecting switch.

arrangements for the load to be controlled by the sensing circuit of the transistor. In the construction shown in FIG. 5, a

relay R is placed in the emitter circuit of the transistor and the contacts of this relay serve to operate the load C.

The microswitch of this invention can thus be used to effect instantaneous control of large currents. This control is effective even though the actual switch current broken by the contact of the ball and plate is small. Devices constructed in ac cordance with the present invention are particularly effective to control electro magnetic clutches and brakes in a duplicating machine in response to the movement of a thin sheet of material, as the material arrives at a particular location in the machine, etc'.

While specific examples of the preferred embodiments of the present invention have been disclosed and described, it is apparent that various modifications within the scope of the invention will become apparent to those'skilled in the art and it is intended that the protection be limited only to the'extent definedin the appended claims.

Iclaim: 1. In a copying machine of the type having a feedplate for receiving sheets of paper, the improvement comprising i a sensing switch for detecting the presence or absence of a sheet of paper on said feedplate and having a normally closed state in the absence of a sheet of paper on said feedplate, and an open state when a sheet of paper is present on said feedplate;

said sensing switch including said feedplate as a first electrically conductive contact, an electrically conductive ball as a second contact, an elongated, resilient metallic strip having a first end supporting said ball to be freely rotating and a second end, and means for securing said second end of said strip to a standard affixed to the copying machine, -the resilience of said strip being sufficient to absorb vibrations of the copying machine;

said ball being supported adjacent said feedplate and normally biased toward said feedplate by said strip such that said ball and saidfeedplate are continuously in electrical contact in the absence of a sheet of paper on said feedplate to place said sensing switch in said closed state and said ball is moved away from said feedplate in response to the presence of a sheet of paper on said feedplate to place said sensing switch in said open state; and

a control circuit connected with said sensing switch including a transistor coupled with a load for operating feed roller means for the copying machine, said transistor having a conductive state to energize said load when said sensing switch is in said open state in response to the presence of a sheet of paper on said feedplate and having a nonconductive state to deenergize said load when said sensing switch is in said closed state in response to the absence of a sheet of paper on said feedplate.

2. The invention as recited in claim 1 wherein said transistor has a base, an emitter and a collector, said load is connected in series with said emitter and said collector, a resistor is connected between said base and said emitter, and said sensing switch is connected in shunt with said resistor whereby said resistor is shunted when said sensing switch is in said closed state to place said transistor in said nonconductive state.

3. The invention as recited in claim 1 wherein sheets of paper are supplied to said feedplate in a predetermined direction, and said second end of said strip is secured at a position remote from said ball with said strip being aligned with said direction of supply.

4. The invention as recited in claim 1 wherein said second end of said strip is displaced from said ball in both horizontal and vertical directions and said strip is curved when said sensing strip is in both said closed and open states.

5. The invention as recited in claim 4 wherein said strip is constructed of a plurality of strips of metallic foil, each of said strips of foil having a different length. 

1. In a copying machine of the type having a feedplate for receiving sheets of paper, the improvement comprising a sensing switch for detecting the presence or absence of a sheet of paper on said feedplate and having a normally closed state in the absence of a sheet of paper on said feedplate, and an open state when a sheet of paper is present on said feedplate; said sensing switch including said feedplate as a first electrically conductive contact, an electrically conductive ball as a second contact, an elongated, resilient metallic strip having a first end supporting said ball to be freely rotating and a second end, and means for securing said second end of said strip to a standard affixed to the copying machine, the resilience of said strip being sufficient to absorb vibrations of the copying machine; said ball being supported adjacent said feedplate and normally biased toward said feedplate by said strip such that said ball and said feedplate are continuously in electrical contact in the absence of a sheet of paper on said feedplate to place said sensing switch in said closed state and said ball is moved away from said feedplate in response to the presence of a sheet of paper on said feedplate to place said sensing switch in said open state; and a control circuit connected with said sensing switch including a transistor coupled with a load for operating feed roller means for the copying machine, said transistor having a conductive state to energize said load when said sensing switch is in said open state in response to the presence of a sheet of paper on said feedplate and having a nonconductive state to deenergize said load when said sensing switch is in said closed state in response to the absence of a sheet of paper on said feedplate.
 2. The invention as recited in claim 1 wherein said transistor has a base, an emitter and a collector, said load is connected in series with said emitter and said collector, a resistor is connected between said base and said emitter, and said sensing switch is connected in shunt with said resistor whereby said resistor is shunted when said sensing switch is in said closed state to place said transistor in said nonconductive state.
 3. The invention as recited in claim 1 wherein sheets of paper are supplied to said feedplate in a predetermined direction, and said second end of said strip is secured at a position remote from said ball with said strip being aligned with said direction of supply.
 4. The invention as recited in claim 1 wherein said second end of said strip is displaced from said ball in both horizontal and vertical directions and said strip is curved when said sensing strip is in both said closed and open states.
 5. The invention as recited in claim 4 wherein said strip is constructed of a plurality of strips of metallic foil, each of said strips of foil having a difFerent length. 